Active electronic integrated circuits for microelectronic devices are typically fabricated by creating a large number of circuits in an array on a silicon wafer. The silicon wafer is typically a thin disk of silicon which undergoes a variety of processes to produce the active circuits in the silicon wafer.
After the active circuits are completely formed, the silicon wafer is separated into the individual integrated circuits in preparation for packaging. The individual circuits are sometimes referred to as “dice” or “dies” and the separating process is sometimes termed “dicing.”
A variety of methods may be used to separate individual circuits on a silicon wafer. It is desirable that whatever method is used for separating the individual circuits that it not requires an excessive amount of space between adjacent circuits to accommodate the mechanical process of separation. Separation processes that allow adjacent circuits to be closer together allow a greater number of devices to be fabricated on a single silicon wafer and thereby reduce the cost per device.
One method of separating the circuits from a silicon wafer is by sawing with a thin abrasive saw. Because silicon wafers are brittle, particularly silicon wafers having a low dielectric constant (low K), the sawing tends to create chipping along the edges of the saw path or kerf. It is necessary to have a sufficient amount of separation between adjacent circuits so that this chipping does not damage the functional parts of the circuit.
Laser scribing may be used as part of the separating process. Laser scribing may be used to create a groove or other surface discontinuity along a line which may be subsequently sawed or broken to complete the separation process. Laser scribing may provide a relatively clean separation of the active circuits at the surface of the silicon wafer. Laser scribing in combination with subsequent sawing may protect the surface of the silicon wafer from the chipping that occurs in the sawing process.
The laser scribing process tends to produce debris that accumulates on the surface of the silicon wafer adjacent to the groove produced by the laser scribing process. This debris must be thoroughly removed to avoid failures in the subsequent packaging operations.
One method of packaging microelectronic circuits is the flip chip process. In flip chip packaging an array of solder balls or die bumps is created on the surface of the silicon wafer to provide a connection to the terminations of the active electronic circuitry. In a subsequent packaging process, the individual circuits are placed on a substrate with the die bumps between the active electronic circuitry and the substrate. By heating this assembly, a soldered connection can be created between a large number of points on the active silicon circuit and the substrate which provides for the external connections of the packaged microelectronic device.
Debris from laser scribing that settles on the die bumps or solder balls will prevent the solder from properly wetting during the process of attaching the silicon chip to the substrate. The failure to properly wet a solder connection may result in a defective device. Therefore, if laser scribing is used, it is necessary that all debris from the laser scribing operation be thoroughly removed from the silicon wafer prior to packaging.